It has in the past been found difficult to obtain consistent, durable, direct seals between glass and stainless steel, for example, 304L stainless steel, the composition of which is approximately 20% chromium, 10% nickel and 70% iron, that has been annealed in a reducing atmosphere in the process of rolling.
It has been discovered that the reducing atmosphere, for example, hydrogen, depletes the chromium from the surface to a depth of 0.0001" or 0.0002" in a 0.015" or 0.03" sheet. The bonding to steel of glass seals, of the type used in making terminals for hermetic motors, for example, is greatly facilitated by a film of chromium oxide. It has been found that by removing the chromium-depleted layer from the stainless steel to a depth at which there is sufficient chromium to produce a chromium oxide film, and forming the film, a highly reliable glass-to-metal seal can be formed consistently.